Insights and comparison of structure–property relationships in propane and propene catalytic combustion on Pd-and Pt-based catalysts

Hydrocarbon combustion is crucial in emission control applications. Developing efficient catalysts where noble metal use is optimized is imperative in this field. Hydrocarbons with varying molecular structures provide different challenges in this process. In this work, propane and propene were chosen as model compounds to compare the active site requirements for their oxidation on Pd- and Pt-based catalysts. A library of uniform Pd/Pt catalysts prepared from colloidal nanoparticle precursors were used to study several important variables including Pd/Pt composition, support, and phase. The effects of these parameters on activity and stability in the presence of steam were carefully evaluated. Our results show that Pt-rich catalysts perform best for both reactions. However, opposite general trends in rate orders, active phase and stability after aging treatments were observed. These differences arise from the distinct rate-limiting steps and coverage between the two reactions, with propene strongly adsorbing on the noble metal surface, while propane has weaker interactions, resulting in different dominating activation steps. Experimental observations were supported by density functional theory calculations, where the activation barriers to crucial elementary steps were found to be different for the two reactions. The results point to different catalytic requirements to activate the two compounds, highlighting the need to optimize catalysts based on contrasting elements. These findings provide insights that can help engineer efficient catalysts for hydrocarbon combustion and optimize the use of precious noble metals.